1. Field of the Invention
The present invention relates to a solid polymer electrolyte fuel cell including a solid polymer electrolyte membrane and a fuel cell electrode. In particular, the present invention relates to solid polymer electrolyte fuel cell in which the solid polymer electrolyte membrane and/or the fuel cell electrode contains a catalyst for disproportionating hydrogen peroxide produce during fuel cell operation.
2. Description of the Related Art
To address environmental pollution problems associated with CO2 discharge and global material resource problems associated with dwindling petroleum reserves, fuel cells that are clean, have a high energy density and require no charging time have been proposed. Fuel cell research and development has progressed rapidly in Japan, and throughout the world. In particular, solid polymer electrolyte fuel cells have been developed as electric power sources for vehicles such as automobiles, because these fuel cells exhibit good low-temperature operation and a high power density.
As solid polymer electrolyte membranes for use in fuel cells, perfluorocarbon polymer membranes having sulfonic groups (trade names: Nafion and Aciplex) have generally been used. It has been confirmed that fuel cells with these membranes exhibit satisfactory power generation performance and durability.
However, cost reductions must be realized if fuel cells are to be of practical use. Relatively inexpensive materials for practical fuel cells may include hydrocarbon-based solid polymer electrolyte membranes. However, hydrogen peroxide that forms on an oxidizer electrode of a fuel cell during power generation causes conventional hydrocarbon-based solid polymer electrolyte membranes to decompose. Thus, fuel cells with these membranes exhibit poor durability.
A method of coating a perfluorocarbon polymer solution on the surface of an oxidizer electrode has been proposed in the article xe2x80x9cDurability of a Hydrocarbon-based Electrolyte Membrane for Use in Solid Polymer Fuel Cellsxe2x80x9d contained in the Journal of Chemical Society of Japan, issued in 1997 (1997, No. 1, p.69). However, this method can merely delay degradation of the hydrocarbon-based solid polymer electrolyte membrane to some extent and can not prevent degradation of the membrane.
The present invention provides a solid polymer electrolyte membrane, a fuel cell electrode and a solid polymer electrolyte fuel cell. The solid polymer electrolyte membrane according to the invention is free from degradation, so that the fuel cell has excellent durability and is available at a reduced cost.
The solid polymer electrolyte membrane can include a hydrocarbon-based solid polymer electrolyte membrane supporting at least one catalyst selected from oxide catalysts, macrocyclic metal complex catalysts and transition metal alloy catalysts. Catalyst in and on the solid polymer electrolyte membrane can lower the activation energy for the disproportionation of hydrogen peroxide. As a result, any hydrogen peroxide entering the solid polymer electrolyte membrane can be decomposed by the catalyst, so that the hydrogen peroxide is prevented from decomposing the solid polymer electrolyte membrane.
The fuel cell electrode can join with a hydrocarbon-based solid polymer electrolyte membrane to form part of a joined body of a fuel cell. The fuel cell electrode can support at least one catalyst selected from oxide catalysts, macrocyclic metal complex catalysts, transition metal alloy catalysts and inorganic salt catalysts. The catalyst can lower the activation energy for the disproportionation of hydrogen peroxide. As a result, any hydrogen peroxide evolved at the fuel cell electrode can be decomposed by the catalyst, so that the hydrogen peroxide is prevented from decomposing the hydrocarbon-based solid polymer electrolyte membrane.
The oxide catalyst can be at least one selected from MnO2, RuO2, ZnO, WO3, MnO2xe2x80x94Al2O3, RuO2xe2x80x94Al2O3, ZnOxe2x80x94Al2O3 and WO3xe2x80x94Al2O3. The oxide catalyst can have a particularly significant catalytic effect on the disproportionation of hydrogen peroxide.
The macrocyclic metal complex catalyst can be at least one selected from iron phthalocyanine (C32H16N8Fe), copper phthalocyanine (C32H16N8Cu), zinc phthalocyanine (C32H16N8Zn) and cobalt phthalocyanine (C32H16N8Co). The macrocyclic metal complex catalyst can have a particularly significant catalytic effect on the disproportionation of hydrogen peroxide.
The transition metal alloy catalyst can be an alloy of one or more transition metals. Preferably, the transition metal alloy catalyst can be a Cuxe2x80x94Ni alloy. The transition metal alloy catalyst can have a particularly significant catalytic effect on the disproportionation of hydrogen peroxide.
The solid polymer electrolyte membrane can include a sulfonic acid-based resin comprising a copolymer of a fluorocarbon-based vinyl monomer and a hydrocarbon-based vinyl monomer. This material can provide a solid polymer electrolyte membrane, or a joined body of a solid polymer electrolyte membrane and fuel cell electrodes, at a reduced cost.
The solid electrolyte membrane fuel cell can include a fuel electrode and an oxidizer electrode positioned on opposite sides of a hydrocarbon-based solid polymer electrolyte membrane containing at least one catalyst selected from oxide catalysts, macrocyclic metal complex catalysts and transition metal alloy catalyst. Since the hydrocarbon-based solid polymer electrolyte membrane can be prevented from decomposition by hydrogen peroxide, a solid polymer electrolyte fuel cell of excellent durability can be obtained.
The solid electrolyte membrane fuel cell can include a fuel electrode and an oxidizer electrode positioned on opposite sides of a hydrocarbon-based solid polymer electrolyte membrane, where the oxidizer electrode contains at least one catalyst selected from oxide catalysts, macrocyclic metal complex catalysts and transition metal alloy catalysts. Since the oxidizer electrode can prevent the hydrocarbon-based solid polymer electrolyte membrane from being decomposed by hydrogen peroxide, a solid polymer electrolyte fuel cell of excellent durability can be obtained.